Use of Soil Survey Data for Regional Soil Water Simulation Models

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Wosten J.H.M
Bouma J
Stofflsen G.H
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A detailed soil survey of an area of 650 ha was used to obtain basic soil physical data for a simulation model of the water regime in the unsaturated zone. Nine major soil horizons were defined for the entire survey area in terms of pedological classification and easily measurable characteristics such as texture, structure, organic matter content, and bulk density. In these horizons multiple measurements of hydraulic conductivity and moisture retention curves were made, yielding average curves. Statistical comparison of the curves showed that only five of the nine major soil horizons were different from a soil-physical point of view. Next, representative soils for the mapping units were transformed into soils composed of a characteristic sequence of some of these five horizons. In this way a simulation map, containing data to be used for simulation of the soil water regime, was formed from the soil map. For a sample area of 125 ha the simulation map contained 41 delineated areas as compared to 110 delineations on the soil map. Sixty independent test borings indicated 80 ± 6% purity comparing borings and the legend of the simulation map. A simulation run for one pedon with the model SW A TRE showed excellent agreement between measured and calculated actual evapotranspiration for the years 1976, 1977 and 1978. Major soil horizons, rather than individual points of observation, were used in this study as carriers of soil physical information, allowing extrapolations based on a limited number of measurements.
Soil Science, 49, p. 1238-1244